Polyesters and other polymeric materials are subject to oxidative polymer degradation during processing and usage due to exposures such as ultraviolet light. More specifically, surface oxidative degradation may occur in exposures to environments containing free radicals. Oxidative degradation is typically hindered by incorporating antioxidants into the material to prevent degradation of the bulk material.
There are two main types of antioxidants, referred to as primary and secondary, and defined by their mode of operation. Primary antioxidants are free radical scavengers that generally terminate free radical chain propagation by donating a hydrogen atom and include hindered phenols and secondary aromatic amines. Secondary antioxidants are hydroperoxide radical decomposers that operate by decomposing the radical into stable non-reactive products and are typically divalent sulfur or trivalent phosphorous.
Antioxidants have also been used to hinder oxidation at the surface of a polymeric material. It has been noted in the art that combining a radical scavenger antioxidant with a peroxide decomposer antioxidant can result in synergistic effects because of complementary but different reaction mechanisms.